Propionation of cellulosic material



Patented May 7, 1935 UNITED STATES PATENTI'OFFICE f 2,000,621 R PROPIONATION 0F CELLULQSIO/MATERIAL Cyril J. Stand and Russel H. Van Dyke, Rochester, N. Y., assignors to Eastman Kodak Com- 7 pany, Rochester, N. Y., incorporation of New York No Drawing. Applicationv Jannary 14, 1933,

Serial No. 651,856

8 Claims. 1 (01. 260- 101) "The present invention relates to the employpreparation of colorless, transparent products such as films or sheets as a truly White product, due'for instance, to the poorer transmission of light of the former. The present invention provides a process for the preparation of propionyl esters of cellulose with technical propionyl supplying materials in which a product is obtained which is substantially free from discoloration and which gives a very clear brilliant solution in the common organic solvents.

One object of our invention is to provide a process for the preparation of propionyl-containing esters of cellulose in which a catalyst is employed which is corrective of the discoloration of the resulting ester which discoloration is sometimes iound in the propionyl-containing esters of cellulose. Another object of our invention is to provide a process for preparing propionyl-containing esters of cellulose, such as celluloseacetate-propionate which allows better control of the esterification reaction than is possible with a commonly employed catalyst such as sulfuric or chlorsulfonic acids when employed in similar fashion. This allows better control of the preparation of a finished product which is more free from unesterified fibers, grain and haze than when for instance, sulfuric acid is employed. Another object of our invention is to provide a process for preparing propionyl-containing esters of cellulose in which the viscosity of the product formed is higher-than in like processes in which zinc chloride or sulfuric acid is employed as the catalyst. This higher viscosity is evidence that the degradation of the cellulose is much less than that which occurs in processes using other catalysts such as zinc chloride or sulfuric acid for example.

We have found that cellulose materialssuch as cotton linters or esterifiable cellulose derivatives may be easily converted into propionyl-containing cellulose esters by treating them in a bath adapted for introducing propionyl groups thereto in the presence of a mixture of S02 and an oxide of nitrogen. The oxides of nitrogen which may be employed for this purpose include nitrogen peroxide or dioxide, nitrogen tetroxide or for that matter any of the higher oxides of nitrogen. Nitric oxide also may be employed in the presence of airor some other source of available oxygen. Q

As pointed out above, our present invention is adapted to the preparation of the propionyl-containing esters of cellulose in general. The employment of our invention for the preparation of cellulose acetate-propionate' is especially contemplated particularly when it is prepared by react-, ing upon cellulose with a reaction mixture containing propionic acid and acetic anhydride togetherwith-the SO -N02 catalyst.

The sulfur dioxide and oxide of nitrogen may be added to the reactionbath in, various .Ways.

For example either one or both of the gases may be dissolved in the bath employed forthe pretreatment of the cellulose or they may be added during the esterification step. If no pretreatment is employed the gases (S02 and N02) will of course be added to the esterification bath proper. The catalyst may be added either by bubbling it into the esterification bath or by first absorbing the gas in one of the ingredients which is to be employed. Various other permutations of the methods of introducing the SO2oxide of nitrogen catalyst will-be obvious to those skilled in the art.

Altho the preparation of the propionyl-contain? ing esters of cellulose in dope form, that isdissolved in the reaction mixture, isprincipally contemplated by our invention, our invention may also be employed in a fibrousf esterification process for the preparation of these esters. Some of the non-solvents which may be employed are carbon tetrachloride, benzene, or a higher ether having a boiling point above 70 C. The employment of the higher ethers in the fibrous esterification of cellulose is disclosed and claimed in Malm and Fletcher application Serial No. 590,509, filed Feb. 2, 1932.

Altho the concentrations of S02 and the oxide of nitrogen in the esterification bath may be varied according to the judgment of the individual operator, we have found that concentrations of approximately 5% to of sulfur dioxide and an equivalent amount of the oxide of nitrogen based on the weight of cellulose employed, will be usually quite suitable.

The following example illustrates the introduction of propionyl groups into cellulose according to the process of our invention:

S02 gas was passed into a mixture of 25 lbs. of propionic acid and lbs. of 93% acetic an-' hydride until about 2 lbs. of the gas was dissolved. This mixture was then added to 10 lbs. of cotton lyzed and found to have a nitrogen content of 1.43%, an apparent acetyl content of 43.85% and a melting point of 254 C. j

The present invention isalso applicable to the preparation of the simple propionic ester of cellulose. For instance in the above example an impelling anhydrid such as chloracetic or analkoxy acetic anhydride could be employed instead of acetic anhydride. As was pointed out above an esterifiable cellulose derivative could be employedas thestarting material of the processvof the present invention, such as a cellulose acetate, nitrate or ether containing free and available hydroxyl groups. When the starting material is to be a cellulose, it is preferred to employ cotton linters, this material being inexpensive and readily susceptible to esterification, however, other celluloses such as reverted cellulose, esterifiable sulfite wood pulp etc. may be employed where desired and compatible.

Various other modifications of our invention made possible by the varying of technical details such as time, temperatures, proportions etc. by those skilled in the art -also come within the scope of our invention and covered by the appended claims.

Whenever the term cellulosic material is employed herein it refers to both materials containing cellulose proper and those containing cellulose which has been reacted upon but which contains free and available hydroxy groups.

What we claim is:

l. The process of preparing a propionyl-containing ester of cellulose which comprises propionating cellulosic material in a bath containing propionyl groups and an impelling anhydride in the presence of a catalyst consisting or sulfur dioxide and an oxide of nitrogen of which the oxygen constitutes m of the compound.

ore than 50% by Weight 2. The process of preparing a propionyl-containing ester of cellulose which comprises propionating cellulosic material in a non-solvent bath containing propionyl groups, an impelling anhydride, and a catalyst consisting of sulfur dioxide and an oxide of nitrogen of which the oxygen constitutes more than 50% by weight of the compound.

3. The process of preparing a propionyl-containing ester of cellulose which comprises propionating cellulosic material in a bath containing propionyl groups and an impelling anhydride in the presence of a catalyst consisting of sulfur dioxide and nitrogen peroxide.

' 4. The process of preparing a propionyl-containing ester of cellulose which comprises propionating cellulosic material in a non-solvent bath containing propionyl groups, an impelling anhydride, and a catalyst consisting of sulfur dioxide and nitrogen peroxide.

-5. The process of-preparing cellulose acetatepropionate which'comprises reacting upon cellulosic material with a bath containing propionic acid, acetic anhydrid and a catalyst consisting of sulfur dioxide and an oxide of nitrogen of which the oxygen constitutes more than 50% by weight of the compound.

6. The process of preparing cellulose acetatepropionate which comprises reacting upon cellulosic material with a bath containing propionic acid, acetic anhydrid and a catalyst consisting of sulfur dioxide and nitrogen peroxide.

'7. The process of preparing a propionyl-containing ester of cellulose which comprises propionating cellulosic material in a bath containing carbon tetrachloride propionyl groups, an impelling anhydride, and a catalyst consisting of sulfur dioxide and an oxide of nitrogen of which the oxygen constitutes more than 50% by weight of the compound.

8. The process of preparing a propionyl-containing ester of cellulose which comprises propionating cellulosic material in a bath containing carbon tetrachloride propionyl groups, an impelling anhydride, and a catalyst consisting of sulfur dioxide and nitrogen peroxide.

CYRIL J. STAUD; RUSSELL H. VAN DYKE. 

